Defmemo

Defmemo is a generic defun form, performing memoization over calls to such defined function. It supports arbitrary lambda lists and multiple return values. (optimize speed)-friendly, otherwise it might have been implemented as in Peter Norvig's PAIP. Preserves arguments and documentation. Memoizing hash table is stored under property :memo of defmemo'ed function.

Usage

Three functions are exported: defmemo (like defun), get-memo and clear-memo (defmemo'ed symbol). Clear-memo is not needed on implementations supporting weak hash tables (via trivial-garbage).

(defmemo fib (n)
  (if (<= n 1)
      1
      (+ (fib (- n 1))
         (fib (- n 2)))))

(fib 100)
; => 573147844013817084101

(get-memo 'fib)
; => #<hash-table :TEST equal :COUNT 101 :WEAKNESS :key>

(hash-table-count (clear-memo 'fib))
; => 0